Zein is a naturally occurring polymeric protein, obtained as a product of industrial corn processing. Compared to most proteins, zein is characterized by a relative deficiency of hydrophilic groups. In zein, the high proportion of nonpolar and acid amide side chains accounts for the solubility of zein in organic solvents and its classification as a prolamine.
Zein is essentially a globular protein in its natural state. Due to its deficiency of hydrophilic groups, zein does not dissolve easily in aqueous solutions. Hence most known processes to make zein fibers employ an alkaline solution to initially hydrate and dissolve the zein, realigning it as desired (e.g., by spinning) and finally stabilizing the new alignment by inducing cross-linking. Most often the alkaline zein solution is wet spun into acidic coagulating baths. Some processes add formaldehyde to the alkaline zein solutions. After spinning, cross-linking can be induced by treatment in coagulating baths containing formaldehyde, and stabilizing with subsequent treatment with formaldehyde. C. B. Croston et al., describe such a process in "Zein Fibers . . . Preparation by Wet Spinning", Industrial and Engineering Chemistry, 37 (12) (1945) 1194-1198. Croston et al. call for zein solutions for spinning containing approximately 13 to 16.5% solids, in the pH range of 11.3 to 12.7. In some experiments, denaturing or gelling agents, such as urea or alcohol were added, or denaturing was effected by applying heat. Formaldehyde was also tested as an additive to the spinning dispersions. The resulting fibers went into a coagulating bath containing sulfuric acid, acetic acid and sometimes zinc sulfate, and were then treated with a mild formaldehyde precuring bath. This precuring bath was found to be necessary prior to the final stretching of the fiber tow which was accomplished in water between two variable speed reels.
The environmental implications of such processes are a major prohibition to commercialization today. The expense of treatment and disposal of the acids, salts and organic compounds required in such processes make production of zein fibers economically impractical.
A few processes have made zein articles from mixtures comprising primarily zein and water. U.S. Pat. No. 2,521,738 discloses a process to make artificial bristles from proteins. The process comprises mixing a protein, e.g., casein or zein, with about 80 to 100 percent of its weight of water, and kneading in a mechanical mixer at 80.degree.-100.degree. C. until a homogeneous plastic gel is obtained. The gel is then converted into fiber bristles by extruding into air and stretching over rolls. The bristles are then treated to subsequent steps of drawing and hardening solutions, which may be a solution of formaldehyde or p-benzo-quinone. This process deliberately effects gelation, since high temperatures and pressures are used, and the bristle fibers formed have tenacities in the range of about 0.8 to about 1.2 grams/denier.
U.S. Pat. No. 3,497,369, discloses a composition of zein which is substantially dry and which upon the addition of warm water, at a temperature of about 60.degree. C. to about 100.degree. C. forms a pliable plastic composition which may be pulled like taffy, molded, or worked with as modeling clay. The composition consists of zein and a small portion of plasticizer such as glyceryl monoricinoleate. About 5 parts of plasticizer for every 75 parts of zein is most preferred. The composition can be molded and allowed to harden to form usable articles, such as jewelry.